What if everyone in the world did a good deed for three people - and what if each of them 'paid it forward' by doing a good deed for three more people, and so on, until the world was a different place? PAY IT FORWARD begins when social studies teacher Reuben St Clair gives his class an extra assignment: implement a plan that will change the world. Trevor, a boy with an active imagination and a loving, though dysfunctional, mother, rises to the challenge.

His plan is this: he'll do something good for three people and tell each that instead of paying him back, they should pay it forward and do a favour for three more people. Trevor's initial attempt seems to fail. But eventually, wondrously, the seeds that Trevor has planted bear fruit in ways that are marvellous to behold and that surprise even Trevor.